V. Yu. Butko

Quantum metallicity in a two-dimensional insulator

One of the most far-reaching problems in condensed-matter physics is to understand how interactions between electrons, and the resulting correlations, affect the electronic properties of disordered two-dimensional systems. Extensive experimental and theoretical studies have shown that interaction effects are enhanced by disorder, and that this generally results in a depletion of the density of electronic states. In the limit of strong disorder, this depletion takes the form of a complete gap in the density of states. It is known that this ‘Coulomb gap’ can turn a pure metal film that is highly disordered into a poorly conducting insulator, but the properties of these insulators are not well understood. Here we investigate the electronic properties of disordered beryllium films, with the aim of disentangling the effects of the Coulomb gap and the underlying disorder. We show that the gap is suppressed by a magnetic field and that this drives the strongly insulating beryllium films into a low-temperature ‘quantum metal’ phase with resistance near the quantum resistance RQ = h/e 2, where h is Plancks constant and e is the electron charge.

Interface phenomena and optical properties of structurally confined InP quantum wire ensembles

Three-dimensional regular ensembles of InP quantum wires have been produced in channels of porous dielectric matrices by metal-organic chemical vapor deposition. These matrices differ both in the diameter of the channels (0.7, 3, and 8 nm) and in their spatial arrangement. The InP layer thickness does not exceed two-three monolayers. A comparative study of Raman, optical absorption, and photoluminescence spectra revealed the dependence of the optical properties of these quantum wires on interface effects, namely, atomic interaction in the wires, wire-matrix, and wire-wire interactions. It is shown that the wire-matrix interaction distorts the InP lattice, broadens the wire electronic density-of-states spectrum in the vicinity of the fundamental gap, and redistributes the relaxation of photoinduced excitations among states belonging to the wire itself and to defects in the matrix bound to the wire.

Electroluminescence of GaPxNyAs1 − x − y nanoheterostructures through a transparent electrode made of CVD graphene

The results of experimental studies aimed at the development of GaPxNyAs1 − x − y alloy nanoheterostructures with a new type of transparent electrode based on CVD graphene are reported. The electroluminescence properties of the structures are studied. High stability of the emission wavelength (2–3 nm) in conditions of increasing temperature (from 12°C to 60°C) and increasing injection current (from 0 A to 1 A) is demonstrated.

Transport properties of graphene in the region of its interface with water surface

The graphene growth by thermal decomposition of silicon carbide at the temperature of ~1400°C in a high vacuum of ~10–6 Torr has been optimized. By Raman spectroscopy, the mean thickness of obtained graphene (2–4 single layers) has been estimated and the presence of high-quality graphene areas in the samples has been demonstrated. It has been found out that the four-point resistance of graphene increases in the region of its interface with water approximately by 25%. For the graphene–water interface in the transistor geometry, with variation in the gate-to-source voltage, the field effect corresponding to the hole type of charge carries in graphene has been revealed.

Fabrication of carbon nanowires by pyrolysis of aqueous solution of sugar within asbestos nanofibers

Carbon nanowires have been fabricated by pyrolysis of an aqueous solution of sugar in nanochannels of asbestos fibers. Electron microscopy demonstrates that the diameter of these nanochannels corresponds to the diameter of the thinnest of the carbon nanowires obtained. Some of these nanowires have a graphite crystal lattice and internal pores. After asbestos is etched out, the carbon nanowires can retain the original shape of the asbestos fibers. Heating in an inert atmosphere reduces the electrical resistivity of the carbon nanowires to ∼0.035 Ω cm.

Electrical transport in graphene with different interface conditions

The effect of the interface on the electrical resistance of graphene chemically deposited from the gas phase (CVD graphene) has been studied in the range from room temperature to the nitrogen boiling temperature. The resistance of a single-layer CVD graphene in the cases of its contacting with Si/SiO2 and GaAs substrates demonstrates a nearly linear metallic temperature dependence with almost the same slope of the normalized curves. This slope corresponds to an increase in the graphene resistance by ~8% when graphene is heated from the boiling nitrogen temperature to room temperature. The four-layer graphene demonstrates a semiconducting temperature dependence in the same temperature range. It has been found that the sputtering of an organic insulator (parylene) on the four-layer graphene increases the slope of this dependence by ~5% and, at room temperature, increases the graphene resistance by ~20%.

Finite bias tunneling anomaly in paramagnetically limited Be films

Abstract We report measurements of the finite bias anomaly in the tunneling density of states of homogeneously disordered superconducting Be films above the paramagnetic limit. To date the anomaly has only been reported in granular Al films and is believed to be a manifestation of a non-perturbative BCS fluctuation mechanism that forms a pseudo-gap near the Zeeman energy. We show that the magnetic field dependence of the anomaly energy in Be films is in good agreement with the recent theory of Aleiner and Altshuler provided the proper normal state Lande g-factor is used.